1. Field of the Invention
The present invention relates to a power-saving discharge lamp, and more particularly, to a discharge lamp such as a cold cathode fluorescent lamp wherein a bulb section is double-sheathed by an internal bulb and an external bulb, and a clearance between both bulbs is evacuated, preventing loss of heat energy when lighted, in order to reduce power consumption.
2. Background Art
FIG. 3 illustrates an example of a power-saving discharge lamp 90 of this kind according to prior arts. The manufacturing method of the power-saving discharge lamp 90 is as follows. Firstly, a conventional discharge lamp 93 is formed by sealing the both ends of an internal bulb 91, inside of which is coated with fluorescent material layer 91a, by a bead stem 92 to which an electrode 92a and a lead wire 92b are attached.
Then, the power-saving discharge lamp 90 is formed by inserting the conventional discharge lamp 93 into an external glass bulb 94, and welding the both ends of the external glass bulb 94 with a gas burner G or the like to double-sheathe the bulb section. In the welding process, the degree of vacuum of the clearance between the internal bulb 91 and the external bulb 94 is raised to 1.times.10.sup.-3 Torr or higher, which improves the heat insulation property between the bulbs 91 and 94, and prevents loss of heat energy when lighted in order to reduce power consumption.
However, in the case with the power-saving discharge lamp 90 constructed according to prior arts, the conventional discharge lamp 93, which is inserted into the external bulb 94, is difficult to support from outside while the external bulb 94 is being welded. Thus after welding of the external bulb 94 is completed, the clearance between the internal bulb 91 and the external bulb 94 tends to be nonuniform as shown in FIG. 4, which not only causes an inaccurate dimension but also, if the nonuniformity goes to an extreme, raises a problem of losing the power-saving effect.
To prevent the nonuniformity of the clearance described above, a cautious and skilled work is required in the welding process of the external bulb 94, as well as a long processing time. Therefore, together with the inaccurate dimension due to the nonuniformity described above, a problem of decrease in productivity also arises, which are the problems to be solved.